1. Field of the Invention
The present invention relates to a method of writing data, and more particularly, to a method of writing data on a ferroelectric layer using a resistive probe.
2. Description of the Related Art
Regarding developments in Internet-related technologies, a writing medium on which a large amount of data including motion pictures can be written (hereinafter, referred to as a “high-density writing medium”) and a portable device for writing the data on the writing medium and reading the written data have lately attracted considerable attention as important products on the writing media market.
A portable nonvolatile data writing device can be categorized as either a solid-state memory device, such as a flash memory, or a disk-type memory device, such as a hard disk.
Since it is anticipated that the needs for primary storage in hand-held devices will reach a capacity of up to several tens of gigabytes in upcoming years, it is difficult for the solid-state memory device to function as a high-density data writing device, probably due to limitations in the lithography technology. Therefore, the solid-state memory device will be used for a device requiring high-speed operations, such as a current personal computer (PC), while the disk-type memory device still will be used as a main storage device.
It is expected that a hard disk of a general magnetic writing type will be developed to have a capacity of up to 10 gigabytes in the near future. However, it is currently impossible to obtain a hard disk that has a higher magnetic writing density than that of the 10-GB hard disk, due to the superparamagnetic effect.
For this reason, a scanning probe has been proposed as a device for writing and reading data, and a memory device formed of a ferroelectric layer has been proposed as a writing medium.
In a technique using a scanning probe, i.e., a scanning probe microscope (SPM), a domain ranging from several nanometers (nm) to several tens of nanometers can be manipulated and probed through a probe.
In recent years, a probe has been manufactured in an array shape through a micro-electro-mechanical system (MEMS) such that parallel reading and writing are enabled to overcome the restrictions of reading and writing speeds.
In a memory device using SPM, written data can be identified by the polarity of electric charges, which are generated on a surface of a ferroelectric layer according to the remnant polarization of the ferroelectric layer, or on a direction of the remnant polarization. The electric charges, which are generated on the surface of the ferroelectric layer according to the remnant polarization, generate an electric field around them. This electric field creates a depletion region or an accumulation region at the end of the probe. The capacitance or resistance of the memory device varies depending on whether the depletion region is formed or the accumulation region is formed and according to the type of probe. The memory device using SPM measures a variation in the capacitance or the resistance to enable reading of data.
This memory device, which operates through SPM and employs a ferroelectric layer as a writing medium, allows higher-density writing of data than a memory device using a magnetic writing medium. However, the memory device using SPM has the following problems.
Specifically, writing data on a ferroelectric layer includes switching a polarization direction of a domain of the ferroelectric layer by applying the same voltage to both ends of a probe. Thus, when the coercive field is large, to ensure thermal stability as the domain size decreases for a high density storage device, the voltage applied to both ends of the probe may cause an electric field that exceeds the dielectric strength of the air gap between the probe and surface of the medium.
Therefore, when the voltage applied to both ends of the probe is too high, since an interval between the probe and the ferroelectric layer is extremely small, an electrical breakdown, such as a corona discharge, may occur therebetween.
Meanwhile, heat assisted magnetic writing (HAMR) has been in the spotlight recently as one of the next-generation magnetic writing technologies. HAMR is being applied to a method and device of writing data on a magnetic writing medium. In the memory device using HAMR, prior to writing data, a predetermined domain of a magnetic writing medium on which the data will be written is heated using a laser. Thereafter, a magnetic field is applied to the heated domain, thereby writing data on the magnetic writing medium.
The heating step and the magnetic field applying step are performed separately. Thus, it takes much time to write data. Accordingly, to shorten the time, the heating step and the magnetic field applying step should be performed at the same time. However, a coil for generating the magnetic field and a laser diode for generating heat cannot be located in the same space. Further, since an interval between a magnetic writing head and a writing medium is very narrow, applying the magnetic field and the heat at the same time is almost impossible.